Huntington's disease is a degenerative, neurological disease that is almost exclusively inherited from a parent. About 1 in 10,000 people, or total about 30,000 people in the United States currently have Huntington's disease and about 150,000 are at risk of having inherited the disease from a parent. Individuals who are at risk of developing Huntington's disease inherit a gene (HD gene) from a parent that codes for a protein now known as the huntingtin protein. The HD gene, whose mutation results in Huntington's disease, is located on chromosome 4 and is characterized by an expanded trinucleotide repeat made up of cytosine, adenine and guanine (CAG). HD is an autosomal dominant disorder. Specifically the HD gene is located on a non-sex-linked chromosome, which means that men and women are equally at risk of inheriting the HD gene and, if the gene is inherited from just one of either parent, the inheriting individual will inevitably develop the disease.
Whether an individual has inherited the HD gene that leads to the development of the disease can be determined by a direct gene test using blood samples. The genetic test counts the number of CAG repeats in the HD gene region. In individuals who do not exhibit the HD gene, the length of the repeat pattern occurs up to 38 times or less. In individuals who inherit the HD gene, the repeat pattern occurs more than 38 times. Only about 1-3% of individuals who develop Huntington's disease do not inherit the disease from a parent.
Previously it was inevitable that an individual who carried the HD gene would at some point in their lives develop the disease. HD results in the genetically programmed degeneration of neurons. The disease causes nerve cells in the striatum of the basal ganglia located deep within the brain, particularly those in the caudate nuclei and the pallidium, and nerve cells in the cortex of the outer surface of the brain, to degenerate via programmed cell death (PCD). PCD is a regulated process by which selective gene expression leads to cell death. The disease eventually leads to uncontrolled bodily movements, mental deterioration and emotional disturbances.
Previously, there was no known means to treat, prevent or otherwise inhibit the development of the disease in individuals who either carry the HD gene or who have already begun developing the disease. In the latter group, only symptomatic therapies were available to target the ensuing symptoms resulting from brain degeneration.